This invention relates to an electrically powered actuator, particularly for controlling a bicycle component, for example a front or rear bicycle derailleur, of the type comprising:
an electrical motor with an output shaft,
a driven shaft rotationally mounted in the casing of the actuator and connected to the output shaft of the electrical motor by means of a reducer, and
a angular position sensor of said driven shaft.
An actuator of the type above is described and illustrated in U.S. Pat. No. 5,480,356 by the Applicant. In this known solution, said driven shaft angular position sensor consists of an encoder, comprising an optical or magnetic reader which co-operates with a plate connected to the driven shaft. Again in this known solution, the actuator is used to control the rear derailleur of a bicycle comprising an articulated parallelogram linkage with the actuator arranged along a diagonal of the parallelogram. The driven shaft is connected to a screw, which engages a worm screw pivotally mounted on one of the vertexes of the parallelogram linkage, so that the rotation of the driven shaft causes the diagonal of the parallelogram linkage to lengthen or shorten, consequently changing the geometry of the parallelogram linkage and shifting the mobile part of the derailleur, which shifts the chain of the bicycle on a plurality of sprockets associated to the hub of the rear wheel of a bicycle. In the past, the Applicant also proposed to use an actuator of the type specified above to control a front bicycle derailleur. In this case, the actuator is connected either directly, or via a transmission, to a lever, which is an integral part of the body formed by one of the arms of the front derailleur parallelogram linkage.
The Applicant also proposed a derailleur (front or rear) of a bicycle equipped with an electrical actuator of the type described above and comprising, instead of the encoder described above, an absolute electrical transducer, typically a rotary potentiometer, associated to said derailleur, for example in position corresponding to one of the articulations of the derailleur parallelogram linkage described in U.S. patent application Ser. No. 09/716,236, filed Nov. 21, 2000.
The objective of this invention is to additionally perfect the previous proposal, making an electrically powered actuator, preferably usable for controlling a bicycle derailleur, but however susceptible of general application, which is distinguished for its elevated characteristics of simplicity and functionality.
In order to attain this objective, this invention refers to an electrically powered actuator, particularly for controlling a bicycle component, for example a front or rear bicycle derailleur, comprising:
an electrical motor with an output shaft,
a driven shaft rotationally mounted in the casing of the actuator and connected to the output shaft of the electrical motor by means of a reducer, and
a angular position sensor of said driven shaft, characterised in that said sensor is a rotary potentiometer associated with said driven shaft inside said actuator casing.
In the preferred form of embodiment of the invention, the reducer is, according to a known technique, an epicyclic reduction gear, comprising an internal gear rigidly connected to the body of the motor, a sun gear connected to the output shaft of the motor coaxially inside the internal gear and a gear set holder rotationally connected to the driven shaft and holding at least one satellite gear freely turning on an axis distanced from the common axis of the sun gear and internal gear, said satellite meshing both the sun gear and the internal gear. The driven shaft is rotationally mounted in a tubular casing projecting from an end of the motor body. Furthermore, the driven shaft is rotationally mounted in said casing by means of at least one rolling bearing of the thrust bearing type. Preferably, the driven shaft is rotationally mounted by means of said thrust bearing and by means of an additional radial ball bearing.
The potentiometer equipping the actuator according to this invention comprises a fixed plate carrying electrical contact tracks on a radial ring side which is fixed which respect to said casing, and at least one sliding contact on the fixed place connected to the driven shaft. The sliding contact is carried by a plate rotationally connected to the driven shaft and axially withheld against the shaft by means of a snap ring mounted on the driven shaft.
Furthermore, seals for protecting from water infiltration are provided in the potentiometer area. According to an additional characteristic, said thrust bearing has a race directly formed on the driven shaft, which prevents axial movements of the driven shaft in a first direction, while the radial bearing is axially withheld by a snap ring mounted on the driven shaft, which prevents axial movement of the latter in a second direction, which is opposite to said first direction.
These constructive details are obviously referred to the preferred form of embodiment described in the accompanying drawings, providing that numerous changes can be implemented, all comprised within the context of the concept characterising this invention.
As illustrated, the actuator according to this invention is preferably usable for controlling the rear or front derailleur of a bicycle, but it can be applied to controlling any other component fitted aboard a bicycle, or any other application.
Consequently, this invention refers both to the actuator per se and, as illustrated in the preferred form of embodiment, to a bicycle transmission system comprising at least one front derailleur or one rear derailleur equipped with said actuator.
This invention will be better explained by the following detailed descriptions with reference to the accompanying figure as non-limiting example, whereas: